A Compact Low-energy Eye-Safe Laser Excitation Based Laser Induced Breakdown Spectroscope (LE-LIBS) Instrument for Chandrayaan-3 Pragyaan Rover

Abstract

A miniaturized low-energy eye-safe laser excitation-based reflective grating-equipped spectroscope, named LE-LIBS (Low-energy Eye-safe Laser Induced Breakdown Spectroscope), was one of the scientific instruments flown in the recent Indian moon mission, Chandrayaan-3. The LE-LIBS, which is the maiden laser-induced plasma spectroscopy instrument to operate on the Moon to date, works on the principles of laser-induced plasma spectroscopy technique and executes in-situ elemental investigations from a close range (205 mm ± 8 mm) in the regions surrounding the Shiv Shakti landing point in the lunar southern higher latitude region. This is the first kind of instrument to function using low-energy (£ 4 mJ) and eye-safe wavelength (1535 ± 1 nm) laser pulses as the ablation force and is equipped with an aberration-corrected concave holographic grating spectrometer (220 nm-800 nm) for spectral discrimination of collected light emitting from the hot-intense plasma with an optical resolution of £ 1 nm. Thorough pre-flight calibration and exhaustive characterization was carried out in a high vacuum environment (~ 1.5 x 10-6 mbar) using diverse standard/certified reference soil powder samples. During the course of instrument development, real-time GUI tools equipped with suitable algorithms are developed in the Python platform to address the data analytics, starting from data pre-processing to element identification and novel approaches, i.e., CF-LIBS, are applied to the ground-data sets for elemental abundance estimation. The first successful LE-LIBS payload operation on the Moon at a site in the southern higher latitude region was performed in the dawn hours of 25th August 2023. The paper reports in brief about the LIBS payload’s instrumentation and ground-performance aspects.